Thermal based drop detection

Abstract

A system comprises a printhead including a nozzle, a temperature sensor and a processor. The temperature sensor detects the temperature of a location of a print surface upon firing the nozzle to eject a drop of printing fluid to the location of the print surface. The processor determines whether the nozzle ejected the drop properly using the detected temperature.

The invention claimed is: 
     
       1. A system, comprising:
 a print head comprising a nozzle; 
 a temperature sensor to detect, upon firing the nozzle to eject a drop of printing fluid to a location of a print surface, a temperature of the location of the print surface when the drop is expected to land at the location, wherein the print surface is a print medium, and wherein the temperature sensor is to determine the temperature of the location of the print medium upon firing the nozzle to eject a drop of printing fluid to the location of the print medium during execution of a print job to generate a printed image on the print medium; and 
 a processor to determine whether the nozzle ejected the drop properly using the detected temperature. 
 
     
     
       2. The system of  claim 1 , wherein the processor is to determine whether the nozzle ejected the drop properly using the detected temperature by determining whether the temperature behavior at the location of the print surface is within a predetermined range and determines that the nozzle did not eject the drop properly if the temperature behavior is not within the predetermined range. 
     
     
       3. The system of  claim 2 , wherein the processor is to determine whether the temperature behavior is within the predetermined range by at least one of:
 determining whether a temperature of the location of the print surface is within an expected temperature range; 
 determining whether a temperature gradient between the temperature of the location of the print surface and an adjacent location of the print surface is within an expected temperature gradient range; and 
 determining whether a temperature gradient between the temperature of the location of the print surface at a time after firing the nozzle and a temperature of the location of the print surface at a time before firing the nozzle is within an expected temperature gradient range. 
 
     
     
       4. The system of  claim 1 , wherein the print head further comprises a nozzle array including a plurality of nozzles, wherein the temperature sensor is to further detect the temperature of a plurality of locations of the print surface upon firing each of the plurality of nozzles to eject a drop of printing fluid to a different one of the locations of the print surface, and the processor is to further determine whether each nozzle ejected the drop properly using the detected temperatures. 
     
     
       5. The system of  claim 4 , comprising a controller to control firing of the plurality of nozzles, wherein the controller is to disable a nozzle of the array of nozzles upon determining that that nozzle did not eject the drop of printing fluid properly. 
     
     
       6. The system of  claim 5 , wherein the controller is to use a nozzle adjacent to the disabled nozzle when printing a print job. 
     
     
       7. A system, comprising:
 a print head comprising a nozzle; 
 a temperature sensor to detect, upon firing the nozzle to eject a drop of printing fluid to a location of a print surface, a temperature of the location of the print surface when the drop is expected to land at the location, wherein the temperature sensor comprises an infrared camera; and 
 a processor to determine whether the nozzle ejected the drop properly using the detected temperature. 
 
     
     
       8. The system of  claim 7 , comprising a servicing station to service the print head, wherein the print surface is a print surface of the servicing station, wherein servicing the printhead comprises firing the nozzle prior to conducting a print job, and wherein the temperature sensor is to detect the temperature of a location of the print surface of the servicing station upon firing the nozzle during servicing thereof. 
     
     
       9. A system, comprising:
 a print head comprising a nozzle; 
 a temperature sensor to detect, upon firing the nozzle to eject a drop of printing fluid to a location of a print surface, the temperature of the location of the print surface when the drop is expected to land at the location; and 
 a carriage carrying the print head, wherein the temperature sensor is attached to the carriage. 
 
     
     
       10. A method of determining whether a nozzle ejected a drop of printing fluid properly, comprising:
 firing a nozzle of a print head to eject a drop of printing fluid to a location of a print surface, wherein the firing and the detecting takes place during execution of a print job to generate a printed image on a print medium; 
 detecting the temperature of the location of the print surface when the drop is expected to land at the location upon firing the nozzle; 
 determining whether the nozzle ejected the drop properly using the detected temperature. 
 
     
     
       11. The method of  claim 10 , comprising determining whether the temperature behavior at the location of the print surface is within a predetermined range and to determine that the nozzle did not eject the drop properly if the temperature behavior is not within the predetermined range by at least one of:
 determining whether to temperature of the location of the print surface is within an expected temperature range; 
 determining whether a temperature gradient between the temperature of the location of the print surface and an adjacent location of the print surface is within an expected temperature gradient range; and 
 determining whether a temperature gradient between the temperature of the location of the print surface at a time after firing the nozzle and a temperature of the location of the print surface at a time before firing the nozzle is within an expected temperature gradient ranges. 
 
     
     
       12. The method of  claim 10 , wherein the firing, the detecting and the determining is conducted for a plurality of nozzles, the method comprising disabling any nozzle determined not to eject the drop of printing fluid properly.